Bug 927349 part 22 - Make AnimationPlayer wait for animations to be rendered before starting; r=jwatt
This patch (finally!) introduces the delayed start behavior. It updates
AnimationPlayer::DoPlay to put animations in the PendingPlayerTracker from
where they are triggered.
This patch also updates nsTransitionManager to set the animation's source
before calling Play as otherwise the AnimationPlayer won't be able to access
the pending player tracker (which it locates by navigating AnimationPlayer ->
Animation (source content) -> target element -> composed doc -> pending player
tracker). In future, when we support setting the AnimationPlayer.source property
we will make this more robust so that the order in which these steps are
performed doesn't matter.
This patch also updates a couple of tests to reflect the fact that
AnimationPlayer will now return the pending state.